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Calcium hydrogen phosphate, commonly known as precipitated calcium phosphate in industry, is abbreviated as precipitated calcium.
Calcium hydrogen phosphate is obtained by reacting a suspension of lime milk or limestone powder with phosphoric acid, and the precipitate is filtered, dried, and crushed. Its main component is calcium hydrogen phosphate dihydrate, with a molecular weight of 172.09. Calcium hydrogen phosphate is a dry, loose powdery crystalline product that is neutral and has low moisture absorption. It is easy to transport, store, and apply. Products made from wet process phosphoric acid may appear gray white or yellow in fertilizer grade due to impurities, and white or gray white in feed grade.
Pure calcium hydrogen phosphate is an important feed additive. Mainly providing phosphorus and calcium, it is usually required to maintain a calcium phosphorus ratio of 1:1-2:1 in feed, and calcium hydrogen phosphate is the most suitable variety. Calcium hydrogen phosphate is a common component of nitrate phosphate fertilizer, ammonium superphosphate and their composite fertilizers. Due to high production costs, the promotion and application of calcium hydrogen phosphate in fertilizers are limited.
Calcium hydrogen phosphate consists of two types: calcium hydrogen phosphate dihydrate and anhydrous calcium hydrogen phosphate, with the commonly used being calcium hydrogen phosphate dihydrate. Calcium dihydrogen phosphate dihydrate, pure substance containing 41.25% phosphorus pentoxide, slightly soluble in water, easily soluble in acid, insoluble in ethanol, and soluble in ammonium citrate solution. Anhydrous calcium hydrogen phosphate, with a pure content of 52.17% phosphorus pentoxide, has a low solubility in citric acid solution.
Calcium dihydrogen phosphate dihydrate is a thermosensitive substance, and crystalline water can be removed by heating. At higher temperatures, it not only dehydrates quickly but also completely. Dicalcium hydrogen phosphate dihydrate is a high concentration goji soluble phosphate fertilizer, suitable as a base fertilizer, suitable for various soils and crops. Its fertilizer efficiency is the same as ordinary superphosphate, and it has a significant effect on acidic soil.
Calcium hydrogen phosphate is produced by neutralization and precipitation of phosphoric acid and lime milk. The production of calcium hydrogen phosphate consists of two steps: the preparation of phosphoric acid solution and the precipitation of calcium hydrogen phosphate.
Fertilizer grade calcium hydrogen phosphate is generally produced by processing phosphate rock with inexpensive and readily available by-product hydrochloric acid, which is relatively economically feasible. Feed grade products require high purity and are usually produced using degummed bone residue, hot process phosphoric acid, or purified wet process phosphoric acid as raw materials.